北美中部大平原半干旱农业生态系统中覆盖作物和灌溉对土壤微生物群落和酶活性的影响（英文）

Cover crops can have beneficial effects on soil microbiology by increasing carbon(C) supply,but these beneficial effects can be modulated by precipitation conditions.The objective of this study was to compare a fallow-winter wheat {TYiticum aestivum L.) rotation to several cover crop-winter wheat rotations under rainfed and irrigated conditions in the semiarid US High Plains.Experiments were carried out at two sites,Sidney in Nebraska,and Akron in Colorado,USA,with three times of soil sampling in2012-2013 at cover crop termination,wheat planting,and wheat maturity.The experiments included four single-species cover crops,a 10-species mixture,and a fallow treatment.The variables measured were soil C and nitrogen(N),soil community structure by fatty acid methyl ester(FAME) profiles,and soil fi-glucosidase,P-glucosaminidase,and phosphodiesterase activities.The fallow treatment,devoid of living plants,reduced the concentrations of most FAMEs at cover crop termination.The total FAME concentration was correlated with cover crop biomass(R = 0.62 at Sidney and 0.44 at Akron).By the time of wheat planting,there was a beneficial effect of irrigation,which caused an increase in mycorrhizal and protozoan markers.At wheat maturity,the cover crop and irrigation effects on soil FAMEs had subsided,but irrigation had a positive effect on the fi-glucosidase and phosphodiesterase activities at Akron,which was the drier of the two sites.Cover crops and irrigation were slow to impact soil C concentration.Our results show that cover crops had a short-lived effect on soil microbial communities in semiarid wheat-based rotations and irrigation could enhance soil enzyme activity.In the semiarid environment,longer time spans may have been needed to see beneficial effects of cover crops on soil microbial community structure,soil enzyme activities,and soil C sequestration.     

Capacity of fatty acid profiles and substrate utilization patterns to describe differences in soil microbial communities associated with increased salinity or alkalinity at three locations in South Australia

 Fatty acid methyl ester (FAME) profiles, together with Biolog substrate utilization patterns, were used in conjunction with measurements of other soil chemical and microbiological properties to describe differences in soil microbial communities induced by increased salinity and alkalinity in grass/legume pastures at three sites in SE South Australia. Total ester-linked FAMEs (EL-FAMEs) and phospholipid-linked FAMEs (PL-FAMEs), were also compared for their ability to detect differences between the soil microbial communities. The level of salinity and alkalinity in affected areas of the pastures showed seasonal variation, being greater in summer than in winter. At the time of sampling for the chemical and microbiological measurements (winter) only the affected soil at site 1 was significantly saline. The affected soils at all three sites had lower organic C and total N concentrations than the corresponding non-affected soils. At site 1 microbial biomass, CO₂-C respiration and the rate of cellulose decomposition was also lower in the affected soil compared to the non-affected soil. Biomarker fatty acids present in both the EL- and PL-FAME profiles indicated a lower ratio of fungal to bacterial fatty acids in the saline affected soil at site 1. Analysis of Biolog substrate utilization patterns indicated that the bacterial community in the affected soil at site 1 utilized fewer carbon substrates and had lower functional diversity than the corresponding community in the non-affected soil. In contrast, increased alkalinity, of major importance at sites 2 and 3, had no effect on microbial biomass, the rate of cellulose decomposition or functional diversity but was associated with significant differences in the relative amounts of several fatty acids in the PL-FAME profiles indicative of a shift towards a bacterial dominated community. Despite differences in the number and relative amounts of fatty acids detected, principal component analysis of the EL- and PL-FAME profiles were equally capable of separating the affected and non-affected soils at all three sites. Redundancy analysis of the FAME data showed that organic C, microbial biomass, electrical conductivity and bicarbonate-extractable P were significantly correlated with variation in the EL-FAME profiles, whereas pH, electrical conductivity, NH₄-N, CO₂-C respiration and the microbial quotient were significantly correlated with variation in the PL-FAME profiles. Redundancy analysis of the Biolog data indicated that cation exchange capacity and bicarbonate-extractable K were significantly correlated with the variation in Biolog substrate utilization patterns. Received: 8 March 2000     

Effect of organic,sustainable, and conventional management strategies in grower fields on soil physical,chemical, and biological factors and the incidence of Southern blight

The objectives of our research were to evaluate the impact of organic, sustainable, and conventional management strategies in grower fields on soil physical, chemical, and biological factors including soil microbial species and functional diversity and their effect on the Basidiomycete plant pathogen Sclerotium rolfsii, causal agent of Southern blight. Soils from 10 field locations including conventional, organic and sustainable farms were sampled and assayed for disease suppressiveness in greenhouse assays, and soil quality indicators. Soils from organic and sustainable farms were more suppressive to Southern blight than soils from conventional farms. Soils from organic farms had improved soil chemical factors and higher levels of extractable C and N, higher microbial biomass carbon and nitrogen, and net mineralizable N. In addition, soil microbial respiration was higher in soils from organic than sustainable or conventional farms, indicating that microbial activity was greater in these soils. Populations of fungi and thermophiles were significantly higher in soils from organic and sustainable than conventional fields. The diversity of bacterial functional communities was also greater in soils from organic farms, while species diversity was similar. Soils from organic and sustainable farms had improved soil health as indicated by a number of soil physical, chemical and biological factors and reduced disease.     

Surface and subsurface microbial biomass, community structure and metabolic activity as a function of soil depth and season

Microbial biomass, size and community structure along with an estimate of microbial activity and soil chemical parameters were determined at three depths in two soils (e.g. sandy loam Ultic Hapludalf and silt loam Mollic Hapludalf) replicated three times under one winter and summer season. Microbial biomass and community structure were estimated from phospholipid-PO₄ content and fatty acid methyl ester (FAME) measurements. Microbial activity and assimilative capacity were estimated using a ³H-acetate incorporation into phospholipids and by incubating the soil samples at the average winter and summer temperatures, 3 and 20 °C, respectively. We found that the size of the microbial biomass in both the surface and the subsurface soils was not significantly affected by the seasonal variation but activity increased by as much as 83% at the summer temperatures in the surface soil. We demonstrated using FAME analysis that for both soils seasonal changes in the subsurface microbial community occurred. These findings suggest that winter conditions will shift the population activity level in both the surface and subsurface systems and the biochemical structure of the community in the subsurface. In all cases, the inorganic chemical properties of the soil, as a function of season, remained constant. The greatly increased activity of microbial population at the higher temperature will favor the capacity of the system to utilize nutrients or organic materials that may enter soil. During low temperature seasons the capacity of either surface or subsurface soils to assimilate materials is generally diminished but the reduction reflects changes in metabolism and not a reduced biomass size.     

Soil microbial community characteristics along an elevation gradient in the Laguna Mountains of Southern California

We sampled soil at four sites in the Laguna Mountains in the western Sonoran Desert to test the effects of site and sample location (between or beneath plants) on fatty acid methyl ester (FAME) and carbon substrate ulilization (Biolog) profiles. The four sites differed in elevation, soil type, plant community composition, and plant percent cover. Soil pH decreased and plant density increased with elevation. Fertile islands, defined as areas beneath plants with greater soil resources than bare areas, are present at all sites, but are most pronounced at lower elevations. Consistent with this pattern, fertile islands had the greatest influence on FAME and Biolog profiles at lower elevations. Based on the use of FAME biomarker and principal components analyses, we found that soil microbial communities between plants at the lowest elevation had proportionally more Gram-negative bacteria than all other soils. At the higher elevation sites there were few differences in FAME profiles of soils sampled between vs. beneath plants. Differences in FAME profiles under plants among the four sites were small, suggesting that the plant influence per se is more important than plant type in controlling FAME profiles. Since microbial biomass carbon was correlated with FAME number (r=0.85,P<0.0001) and with FAME named (r=0.88,P<0.0001) and total areas (r=0.84,P<0.0001), we standardized the FAME data to ensure that differences in FAME profiles among samples were not the result of differences in microbial biomass. Differences in microbial substrate utilization profiles among sampling locations were greatest between samples taken under vs. between plants at the two lower elevation sites. Microbial substrate utilization profiles, therefore, also seem to be influenced more by the presence of plants than by specific plant type.     

冬季作物对水稻生育期土壤微生物量碳、氮的影响

选取我国南方4种冬季作物黑麦草、紫云英、油菜、马铃薯,以冬闲田作对照,对水稻生育期土壤微生物量碳（SMBC）和土壤微生物量氮（SMBN）的短期内动态变化进行了研究。结果表明,早稻田翻耕前,冬季作物处理土壤SMBC和SMBN与冬闲田存在显著差异(P0.05),黑麦草处理SMBC为398.5 mg/kg,显著高于其他作物;紫云英处理SMBN最高,为97.8 mg/kg。在早稻整个生育期,黑麦草处理SMBC显著高于其他处理,晚稻生长过程中各处理无显著差异。冬季作物对稻田土壤微生物商(MQ)的影响,随着水稻生长发育进程有不同程度的变化,黑麦草处理在早稻整个生育期高于冬闲田。     

Arable weeds,cover crops,and tillage drive soil microbial community composition in organic cropping systems

Cover crops have traditionally been used to reduce soil erosion and build soil quality, but more recently cover crops are being used as an effective tool in organic weed management. Many studies have demonstrated microbial community response to individual cover crop species, but the effects of mixed species cover crop communities have received less attention. Moreover, the relationship between arable weeds and soil microbial communities is not well understood. The objective of this study was to determine the relative influence of cover crop diversity, early-season weed communities, and tillage on soil microbial community structure in an organic cropping system through the extraction of fatty acid methyl esters (FAMEs). A field experiment was conducted between 2009 and 2011 near Mead, NE where spring-sown mixtures of zero (control), two, and eight cover crop species were included in a sunflower–soybean–corn crop rotation. A mixture of four weed species was planted in all experimental units (excluding the no-cover control), and also included as an individual treatment. Cover crops and weeds were planted in late-March, then terminated in late-May using a field disk or sweep plow undercutter, and main crops were planted within one week of termination. Three (2009) or four (2010–11) soil cores were taken to a depth of 20 cm in all experimental units at 45, 32, and 25 days following cover crop termination in 2009, 2010, and 2011, respectively. Total FAMEs pooled across 2009 and 2010 were greatest in the two species mixture–undercutter treatment combination (140.8 ± 3.9 nmol g⁻¹) followed by the eight species mixture–undercutter treatment combination (132.4 ± 3.9 nmol g⁻¹). Abundance of five (2009 and 2010) and seventeen (2011) FAME biomarkers was reduced in the weedy treatment relative to both cover-cropped treatments and the no-cover control. In 2009 and 2010, termination with the undercutter reduced abundance of most actinomycete biomarkers while termination with the field disk reduced abundance of C18:1(cis11) and iC16:0. Canonical discriminant analysis of the microbial community successfully segregated most cover crop mixture by termination method treatment combinations in 2009 and 2010. Microbial communities were most strongly influenced by the presence and type of early-spring plant communities, as weeds exerted a strong negative influence on abundance of many key microbial biomarkers, including the AMF markers C16:1(cis11) and C18:1(cis11). Weeds may alter soil microbial community structure as a means of increasing competitive success in arable soils, but this relationship requires further investigation.     

Long-term fertilization regimes influence FAME profiles of microbial communities in an arable sandy loam soil in Northern China

Soil samples collected from a long-term (19-year) experimental field with seven treatments were analyzed for fatty acids methyl esters (FAMEs) to determine fertilization regime effects on microbial community structure in sandy loam soils. The amounts of FAMEs in bacteria, actinomycetes, and fungi were highest with the two organic manure (OM)-fertilized treatments (OM and 1/2 OMN – half OM plus half mineral fertilizer), lowest with the NK treatment, and fell in the middle levels with three mineral P-fertilized treatments (NPK, NP and PK) and the control with no fertilizer (CK), with the exception of fungi which showed no significant difference among the five treatments without OM fertilization. Principal component analysis of FAME patterns indicated that NPK was not significantly different from CK, but the two manure-containing treatments and the P-deficiency treatment (NK) were significantly different from CK and NPK. Redundancy analysis plot showed that FAME amounts significantly correlated to soil organic C and total N contents, while soil available P and total P contents, which were greatly decreased by the NK treatment, also had positive and substantial effects on soil microbial FAMEs. The results demonstrated the importance of P fertilization as well as organic manure in maintaining soil microbial biomass and impacting community structure.     

Nitrate leaching: modifying the loss from mineralized organic matter

The impact on nitrate leaching of agronomic practices designed to immobilize nitrogen in autumn and winter was investigated over 4 years. Experimental treatments (reducing tillage depth, incorporating harvest residues, reducing fertilizer N by growing unfertilized grass or by spring-sown rather than autumn-sown crops) were compared with a control treatment in which autumn crops were sown after burning harvest residues, mouldboard ploughing and seedbed preparation. Winter cover cropping was also compared with winter fallowing. In the first year, incorporation of harvest residues or reducing tillage depth significantly decreased nitrate leaching compared with the control. Unfertilized grass did not affect leaching in the first winter but significantly decreased it in years 2 and 3. When winter cover crops were grown, nitrate leaching was never less than that under an autumn-sown cereal, and in the subsequent year leaching could be significantly greater. Winter fallowing caused the most nitrate leaching over the year. In the winter following a spring-sown crop, leaching under an autumn-sown crop greatly increased. Summed over 4 years, most leaching occurred with the winter fallow—spring cropping treatment; it was 18% more than where a winter cover crop preceded the spring crop. Reducing tillage depth or incorporating harvest residues did not significantly decrease leaching. Unfertilized grass ley followed by an autumn-sown cereal in the fourth year was the only treatment that significantly decrease leaching. Unfertilized grass ley followed by an autumn-sown cereal in the fourth year was the only treatment that significantly reduced leaching loss compared with the control. Incorporating harvest residues resulted in a balance between annual N inputs and outputs. All other treatments required substantial net annual N mineralization to balance annual inputs and outputs.     

Soil microbial communities under different soybean cropping systems: Characterization of microbial population dynamics, soil microbial activity, microbial biomass, and fatty acid profiles

This work analyzes the direct effect of soil management practices on soil microbial communities, which may affect soil productivity and sustainability. The experimental design consisted of two tillage treatments: reduced tillage (RT) and zero tillage (ZT), and three crop rotation treatments: continuous soybean (SS), corn–soybean (CS), and soybean–corn (SC). Soil samples were taken at soybean planting and harvest. The following quantifications were performed: soil microbial populations by soil dilution plate technique on selective and semi-selective culture media; microbial respiration and microbial biomass by chloroform fumigation-extraction; microbial activity by fluorescein diacetate hydrolysis; and fatty acid methyl ester (FAME) profiles. Soil chemical parameters were also quantified. Soil organic matter content was significantly lower in RT and SS sequence crops, whereas soil pH and total N were significantly higher in CS and SC sequence crops. Trichoderma and Gliocladium populations were lower under RTSS and ZTSS treatments. Except in a few cases, soil microbial respiration, biomass and activity were higher under zero tillage than under reduced tillage, both at planting and harvest sampling times. Multivariate analyses of FAMEs clearly separated both RT and ZT management practices at each sampling time; however, separation of sequence crops was less evident. In our experiments ZT treatment had highest proportion of 10Me 16:0, an actinomycetes biomarker, and 16:1ω9 and 18:1ω7, two fatty acids associated with organic matter content and substrate availability. In contrast, RT treatment had highest content of branched biomarkers (i15:0 and i16:0) and of cy19:0, fatty acids associated with cell stasis and/or stress. As cultural practices can influence soil microbial populations, it is important to analyze the effect that they produce on biological parameters, with the aim of conserving soil richness over time. Thus, in a soybean-based cropping system, appropriate crop management is necessary for a sustainable productivity without reducing soil quality.     

Long term tillage,cover crop,and fertilization effects on microbial community structure,activity: Implications for soil quality

Conservation agriculture practices, such as reduced tillage, cover crops and fertilization, are often associated with greater microbial biomass and activity that are linked to improvements in soil quality. This study characterized the impact of long term (31 years) tillage (till and no-till), cover crops (Hairy vetch- Vicia villosa and winter wheat- Triticum aestivum, and a no cover control), and N-rates (0, 34, 67 and 101 kg N ha⁻¹) on soil microbial community structure, activity and resultant soil quality calculated using the soil management assessment framework (SMAF) scoring index under continuous cotton (Gossypium hirsutum) production on a Lexington silt loam in West Tennessee.No-till treatments were characterized by a significantly greater (P < 0.05) abundance of Gram positive bacteria, actinomycetes and mycorrhizae fungi fatty acid methyl ester (FAME) biomarkers compared to till. Saprophytic fungal FAME biomarkers were significantly less abundant (P < 0.05) under no-till treatments resulting in a lower fungi to bacteria (F:B) ratio. Key enzymes associated with C, N & P cycling (β-glucosidase, β-glucosaminidase, and phosphodiesterase) had significantly higher rates under no-till relative to till, corresponding to significantly greater (P < 0.05) soil C and N, extractable nutrients (P, K and Ca) and yields. Mycorrhizae fungi biomarkers significantly decreased (P < 0.05) with increasing N-rate and was significantly less (P < 0.05) under the vetch cover crop compared to wheat and no cover. Treatments under vetch also had significantly higher β-glucosaminidase and basal microbial respiration rates compared to wheat and no cover.Consequently, the total organic carbon (TOC) and β-glucosidase SMAF quality scores were significantly greater under no-till compared to till and under the vetch compared to wheat and no cover treatments, resulting in a significantly greater overall soil quality index (SQI).Our results demonstrate that long-term no-till and use of cover crops under a low biomass monoculture crop production system like cotton results in significant shifts in the microbial community structure, activity, and conditions that favor C, N and P cycling compared to those under conventional tillage practices. These practices also led to increased yields and improved soil quality with no-till having 13% greater yields than till and treatments under vetch having 5% increase in soil quality compared to no cover and wheat.     

Soil microbial biomass and community composition as affected by cover crop diversity in a short‐term field experiment on a podzolized Stagnosol‐Cambisol

Background: Cover cropping appears as a useful land management practice with numerous benefits for ecosystem functions. Aim: The objectives of this study were to determine the effects of different winter cover crops on soil microbial biomass, activity, and community composition in intensively managed agriculture systems as function of cover crop diversity. Methods: For this purpose, an on‐farm experiment was conducted at a podzolized Stagnosol‐Cambisol during seven months growing oil radish as single cover crop and five different cover crop mixtures comprising 5 to 13 plant species. A fallow treatment was used as control. Phospholipid fatty acids were used to determine the soil microbial biomass and soil microbial community composition. Basal respiration of the soil microorganisms was measured as a proxy for microbial activity. Results: The results show that none of the cover crop mixture could increase soil organic carbon or total nitrogen content. Three cover crop mixtures and oil radish as single cover crop significantly increased soil microbial biomass by about 50% and all of the investigated cover crops significantly increased microbial respiration and metabolic quotient by 50–150%. Only highly diverse cover crop mixtures significantly increased individual microbial groups such as Gram‐positive and Gram‐negative bacteria, actinobacteria, and saprotropic and mycorrhizal fungi by about 20% compared to the control. However, the ratio of fungi to bacteria was not influenced by any of the cover crop mixtures under study. Conclusion: These findings corroborate that aboveground plant diversity is linked to belowground microbial diversity.     

冬季覆盖作物残茬还田对双季稻田土壤有机碳和碳库管理指数的影响

研究冬季不同覆盖作物残茬还田后稻田土壤总有机碳、活性有机碳含量和碳库管理指数的变化, 对合理利用冬闲稻田, 发展冬季覆盖作物, 以及科学评价不同种植模式具有重要意义。本研究以不同冬季覆盖作物-双季稻定位试验为研究对象, 采用田间小区试验方法, 分析了黑麦草-双季稻(T1)、紫云英-双季稻(T2)和油菜-双季稻(T3) 3种种植模式不同冬季覆盖作物残茬还田后对土壤耕层(0~20 cm)总有机碳、活性有机碳含量的影响, 并计算了各处理的碳库活度、碳库活度指数、碳库指数和碳库管理指数。结果表明, 与冬闲-双季稻(对照)相比, T1、T2和T3处理的冬季覆盖作物残茬还田均提高了稻田土壤总有机碳和活性有机碳含量, 其大小顺序均表现为T2>T1>T3>CK。其中, 各处理稻田土壤总有机碳含量均显著高于对照, 早稻收获时T1、T2和T3处理土壤总有机碳含量两年平均分别比对照增加6.73%、10.53%和4.79%, 晚稻收获时两年平均分别增加4.16%、6.20%和2.37%; T1和T2 处理土壤活性有机碳含量均显著高于对照, 早稻收获时两年平均分别比对照增加10.52%和21.52%, 晚稻收获时两年平均分别增加11.99%和15.59%。冬季覆盖作物残茬还田提高了土壤碳库活度、碳库活度指数、碳库指数和土壤碳库管理指数, 其大小顺序均表现为T2>T1>T3。总的来说, 各处理中以紫云英残茬还田的效果为最好, 黑麦草和油菜残茬还田的效果次之。     

Soil Microbial Community Diversity and Its Relationships with Geochemical Elements under different Farmlands in Shouguang,China

The aims of this study were to investigate soil microbial community characteristics and their interrelationships with soil geochemistry under different farmlands in Shouguang, China. The traditional dilution plate counts, BIOLOG system, and fatty acid methyl ester (FAME) analyses were used to assess microbial populations, substrate utilization, and fatty acid profiles. The number of aerobic heterotrophic bacteria varied significantly among untilled land, maize, and mungbean fields. The amounts of actinomycetes, fungal fatty acids, and Gram-positive/Gram-negative bacteria ratios varied greatly among celery, tomato, and aubergine fields. In the tomato field, the soil microbial community characteristics were significantly different from other fields. Principal component analysis of BIOLOG and FAME data revealed differences in the catabolic capability and fatty acid profiles of soil microbial communities among different farmlands. Spearman correlation analyses showed that in these sand clay soils of Shouguang, microbial communities in different farmlands were closely correlated with soil geochemical elements, moisture, and organic matter.     

渭北旱塬不同田间管理措施下冬小麦产量及水分利用效率

水分是限制旱地作物产量最主要的因素,提高自然降水利用效率是增加旱地作物产量的有效途径。2001～2003年在渭北旱塬粉砂壤土上的田间试验研究表明,不同田间管理措施对冬小麦的产量及水分利用效率有显著的影响。秸秆覆盖不仅增加雨水入渗,提高上层土壤含水量,而且促进水分向下运输。在覆盖第二年小麦产量较常规种植显著增加,同时覆盖下土壤有机质含量有较快增加的趋势。夏季休闲期种植填闲作物将不影响下一季作物的水分状况,短期内填闲作物对土壤有机质,小麦产量及水分利用效率也没有影响。     

Taxonomic and functional diversity of the soil microbiome recruited from alternative crops in a rotation system

Intensive cropping is considered to contribute to negative effects both on soil physiochemical properties and on long-term grain yield, which can be alleviated by appropriate crop rotations. The soil microbial community can vary with different crop rotations, which in turn affect soil quality and grain yield. Therefore, it is of great significance to elucidate the response of the soil microbial community to crop rotation. In this study, the structural and functional changes of microbial community in different crop rotations were analyzed using high-throughput sequencing and metagenomics analysis in a field experiment. The continuous winter wheat-summer maize cropping system was the control, and three crop rotations were established in October 2016 as follows: (1) spring peanut→winter wheat-summer maize, (2) winter wheat-summer peanut→winter wheat-summer maize and (3) spring sweet potato→winter wheat-summer maize. Soil samples were collected in September 2021 for soil microbial assessment. The results showed that the relative abundance of Actinobacteriota in the soil of spring sweet potato→winter wheat-summer maize was significantly higher (15.2%) than that in the control. The relative abundance of Ascomycota was significantly higher (19.8%–23.2%) in the soil following crop rotation compared with the control. Compared with the control, spring peanut→winter wheat-summer maize enriched energy metabolism genes, and spring sweet potato→winter wheat-summer maize reduced the genes related to plant–pathogen interaction. Compared with the control, crop rotation significantly decreased the relative abundance of the inorganic phosphorus solubilization gene (gcd) and the phosphorus transport gene (upgE) and increased the abundance of organic phosphorus mineralization genes (phoA and phyA). Based on these results, we concluded that the composition of the soil microbial community and functional genes can be altered by crop rotation, and spring peanut→winter wheat-summer maize and spring sweet potato→winter wheat-summer maize had more significant effects. This study provided a reference for the selection of crop rotations in the North China Plain based on the soil microbial community and its function.     

Hydraulic conductivity, residue cover and soil surface roughness under different tillage systems in semiarid conditions

The objective of this study was to investigate the effect of tillage and cropping system on near-saturated hydraulic conductivity, residue cover and surface roughness to improve soil management for moisture conservation under semiarid Mediterranean conditions. Three tillage systems were compared (subsoil tillage, minimum tillage and no-tillage) under three field situations (continuous crop, fallow and crop after fallow) on two soils (Fluventic Xerochrept and Lithic Xeric Torriorthent). Soil under no-tillage had lower hydraulic conductivity (5.0 cm day⁻¹) than under subsoil tillage (15.5 cm day⁻¹) or minimum tillage (14.3 cm day⁻¹) during 1 of 2 years in continuous crop due to a reduction of soil porosity. Residue cover at sowing was greater under no-tillage (60%) than under subsoil or minimum tillage (<10%) in continuous crop. Under fallow, residue cover was low (10%) at sowing of the following crop for all tillage systems in both soils. Surface roughness increased with tillage, with a high value of 16% and decreasing following rainfall. Under no-tillage, surface roughness was relatively low (3–4%). Greater surface residue cover under no-tillage helped conserve water, despite indications of lower hydraulic conductivity. To overcome the condition of low infiltration and high evaporation when no-till fallow is expected in a cropping sequence, either greater residue production should be planed prior to fallow (e.g. no residue harvest) or surface tillage may be needed during fallow.     

Crop rotation and seasonal effects on fatty acid profiles of neutral and phospholipids extracted from no‐till agricultural soils

Analysis of phospholipids (PLFA) and neutral lipids fatty acids (NLFA) was used to characterize no‐till productive agricultural soils associated with different crop rotation levels, replicated across a 400 km transect in the Argentinean pampas, during two sampling seasons, summer and winter. High rotation (HR) management consisted in maize–wheat–soybean intense rotation including cover crops. Low rotation (LR) management trend to soybean monocultures. Soils from nearby natural environments (NEs) were used as references. Fatty acids concentration in soils (nmol/g) decreased c.a. 50% from summer to winter differentially according to soil treatment being the smallest decrease in HR management 35%. Both PLFA and NLFA profiles showed strong potential to discriminate between different land uses. In winter samples, some rare or unknown fatty acids were relevant for the discrimination of agricultural practices while NLFA 20:0 appears to be a good marker of HR soils despite season or location. The PLFA‐based taxonomic biomarkers for total bacteria, Gram‐negative bacteria and arbuscular mycorrhiza showed a significant trend NE>HR>LR in the winter sampling. HR management was also characterized by high levels of NLFA in winter samples as if high crop rotation improves lipids reserves in soil during winter more than in monocropping soil management. In conclusion, PLFA and particularly NLFA profiles appear to provide useful and complementary information to obtain a footprint of different soil use and managements, improving soil biochemistry characterization tools.     

Organic nitrogen cycling microbial communities are abundant in a dry Australian agricultural soil

Some microbial nitrogen (N) cycling processes continue under low soil moisture levels in drought-adapted ecosystems. These processes are of particular importance in winter cropping systems, where N availability during autumn sowing informs fertilizer practices and impacts crop productivity. We evaluated the organic and inorganic N-cycling communities in a key cropping soil (Vertosol), using a controlled-environment incubation study that was designed to model the autumn break in south Australian grain growing regions. Soils from wheat, lucerne, and green manure (disced-in vetch) rotations of the Sustainable Cropping Rotations in Mediterranean Environments trial (Victoria, Australia) were collected during the summer when soil moisture was low. Microbial community structure and functional capacity were measured both before and after wetting (21, 49, and 77 days post-wetting) using terminal restriction fragment length polymorphism measures of bacterial and fungal communities, and quantitative PCR of nitrogen cycling genes. Quantified genes included those associated with organic matter decomposition (laccase, cellobiohydrolase), mineralization of N from organic matter (peptidases) and nitrification (bacterial and archaeal ammonia monooxygenase and nitrite oxidoreductase). In general, the N cycling functional capacity decreased with soil wetting, and there was an apparent shift from organic-N cycling dominance to autotrophic mineral-N cycling dominance. Soil nitrate levels were best predicted by laccase and neutral peptidase genes under drought conditions, but by neutral peptidase and bacterial ammonia monooxygenase genes under moist conditions. Rotation history affected both the structural and functional resilience of the soil microbial communities to changing soil moisture. Discing in green manure (vetch) residues promoted a resilient microbial community, with a high organic-N cycling capacity in dry soils. Although this was a small-scale microcosm study, our results suggest that management strategies could be developed to control microbial organic-N processing during the summer fallow period and thus improve crop-available N levels at sowing.     

Identifying indicators of C and N cycling in a clayey Ultisol under different tillage and uses in winter

Although tropical and subtropical environments permit two cropping cycles per year, maintaining adequate mulching on the soil surface remains a challenge. In some cases, leaving soils fallow during the winter as an agricultural practice to control pathogens contributes to reduce soil mulching. The aim of this study was to assess attributes associated with C and N cycling in a soil under conventional and no-tillage management, with contrasting uses in winter: black oats (Avena strigosa Schreb) as cover crop or fallow. No-tillage increased total C and N, irrespective the winter crop. Cropping black oats under no-tillage resulted in more microbial biomass C and N, and glutaminase activity (15.2%, 65.2%, and 24%, respectively) than no-tillage under fallow. Under conventional tillage, winter cropping did not affect the attributes under study. Available P was higher in the no-tillage system (9.2–12.3 mg kg⁻¹), especially when cropped with black oats, than in the conventional tillage system (4.8–6.6 mg kg⁻¹). A multivariate analysis showed strong relationships between soil microbiological and chemical attributes in the no-tillage system, especially when cropped with black oats. Soil pH, dehydrogenase and acid phosphatase activities were the most effective at separating the soil use in winter. Microbial N, total N, microbial to total N ratio, available P, metabolic quotient (qCO₂), and glutaminase activity were more effective at separating soil management regimes. The no-tillage system in association with winter oat cropping stimulated the soil microbial community, carbon and nutrient cycling, thereby helping to improve the sustainability of the cropping system.